The present invention relates to a boot disposed between two members, movable relative to each other, such as a buckle of a seat belt device installed for a seat of a vehicle such as an automobile, and a buckle supporting member fixed to a vehicle body for movably supporting the buckle when necessary. The boot contracts at least when subjected to pressure exceeding a predetermined value. Also, the present invention relates to a seat belt device employing the boot.
Bellow-shaped boots capable of expansion and contraction have been conventionally disposed between two members that are movable relative to each other in an axial direction, thereby protecting a portion between the two members. Such boots are used in various applications like, for example, a seat belt device installed to a seat of a vehicle such as an automobile.
Generally, the seat belt device comprises a seat belt retractor, not shown here (but shown in FIG. 1 later), which is fixed to a vehicle body near a vehicle seat and normally accommodates a seat belt to allow the seat belt to retract and withdraw and to prevent the withdrawal of the seat belt in an emergency such as a vehicle collision to restrain and protect an occupant in the vehicle seat; the seat belt for restraining the occupant wearing the seat belt that extends from the seat belt retractor and whose end is connected to an anchor fixed to a portion of the vehicle body on an outer side of the vehicle seat; a buckle fixed to, for example, a portion of the vehicle body on an inner side of the vehicle seat; and a tongue that is slidably disposed to the seat belt and can be engaged with or released from the buckle. The seat belt is withdrawn to extend across the shoulder, chest, and lap of the occupant and the tongue is latched to the buckle, whereby the seat belt is worn by the occupant.
When the occupant wears the seat belt, in a normal state, the seat belt is lightly retracted by the seat belt retractor to fit the occupant""s body to such an extent that the occupant does not feel pressure and in such a manner as to allow the retraction and withdrawal of the seat belt. In the event of emergency such as a vehicle collision at which large deceleration is exerted on the vehicle, the occupant tends to move forward due to a large inertia force. However, the seat belt is stopped from being withdrawn, thereby restraining and protecting the occupant.
Some conventional seat belt devices have a pretensioner that is activated in the case of emergency such as a vehicle collision to pull the seat belt, thereby improving the restraint performance and thus rapidly restraining the occupant with increased restraining force. The pretensioner is normally installed in the seat belt retractor, and in some cases installed to the buckle itself or to the anchor.
For example, in the case that the pretensioner is installed to the buckle, as shown in FIGS. 5(a), 5(b), a buckle 2 is supported by a buckle supporting member 1 that is fixed to a vehicle floor (not shown) in such a manner that the buckle 2 is movable relative to the buckle supporting member 1 in the longitudinal direction (the vertical direction in FIGS. 5(a), 5(b)). The buckle supporting member 1 and the buckle 2 are the two members movable relative to each other according to the present invention. One end of a wire 3 is connected to the buckle 2 and the other end of the wire 3 is connected to a piston of a buckle pretensioner (not shown). Generally, the buckle pretensioner is structured to generate high-pressure reaction gas as a result of a reaction of a reactant in the event of emergency such as a vehicle collision. The pressure of the reaction gas actuates the piston of the buckle pretensioner so as to pull the wire 3 with relatively large force.
Further, a boot 4 is arranged to cover the wire 3 between the buckle supporting member 1 and the buckle 2. The boot 4 is made of a resin or a rubber and formed in a cylindrical shape. In addition, the boot 4 has a bellow-shaped shrinkable portion composed of mountainous convexities and concavities with triangular cross sections. In this case, the cross sections (cut in a direction perpendicular to the longitudinal direction of the boot 4, not shown) of the shrinkable portion at the respective four triangular convexities (the number of concavities is three) have the same shape and dimension.
That is, in a vertical section shown in FIG. 5(a) passing through the center of a cross section of the boot 4, a straight line xcex1 in the longitudinal direction connecting the tops 4a of the convexities at one side (left side in FIG. 5(a)) and a straight line xcex2 in the longitudinal direction connecting the tops 4a of the convexities at the other side (right side in FIG. 5(a)) are parallel to each other. The boot 4 can freely expand and contract when it is not attached to the buckle.
In a normal state, the boot 4 is held in an expanded state as shown in FIG. 5(a). The buckle 2 is substantially fixed to the vehicle body by the wire through the boot 4. As the buckle pretensioner is actuated in the event of emergency such as a vehicle collision in the state that the seat belt is worn, i.e. the tongue is latched to the buckle, the wire 3 is pulled with the relatively large force as mentioned above, so that the boot 4 deforms in the longitudinal direction to contract as shown in FIG. 5(b). Therefore, the buckle 2 is moved toward the vehicle body (downward in FIGS. 5(a), 5(b)), thereby pulling the seat belt extending across the occupant and thus increasing the restraint force on the occupant by the seat belt.
To improve the restraint performance by the seat belt for the occupant in the event of emergency, the amount of the stroke movement of the buckle 2 upon the actuation of the buckle pretensioner is required as large as possible. For this purpose, the contraction amount in the longitudinal direction of the boot 4 must be made as large as possible.
However, in the aforementioned conventional boot 4, the convexities of the boot 4 contact each other to be overlapped in the contracting direction (the longitudinal direction) as shown in FIG. 5(b), thus the boot 4 can not contract further from this state. The maximum contraction amount of the boot 4 is limited by a length xe2x80x9caxe2x80x9d of the overlapped convexities in the longitudinal direction. Therefore, the smaller the length xe2x80x9caxe2x80x9d is, the larger the maximum contraction amount is. In addition, the length xe2x80x9caxe2x80x9d is determined by a thickness xe2x80x9ctxe2x80x9d of the boot 4.
It is possible that the thickness xe2x80x9ctxe2x80x9d of the boot 4 is reduced in order to increase the contraction amount of the boot 4. However, the reduction in thickness xe2x80x9ctxe2x80x9d results in lower strength of the boot 4. That is, there is a limit of reducing the thickness xe2x80x9ctxe2x80x9d. Accordingly, the reduction in the thickness xe2x80x9ctxe2x80x9d of the boot 4 will not result in a large increase in the contraction amount of the boot 4.
As mentioned above, the aforementioned conventional boot 4 has a problem that there is a limit of increasing the maximum contraction amount. Accordingly, there is a limit of increasing the stroke of the buckle 2, and it is thus impossible to greatly improve the restraint performance for the occupant by the buckle pretensioner.
Further, in the case of the pretensioner installed to the anchor, there is also a limit of increasing the maximum amount of the boot contraction in the same manner as the aforementioned case of the buckle pretensioner. Accordingly, there is a limit of pulling the seat belt and it is thus very difficult to greatly improve the restraint performance by the anchor pretensioner for the occupant.
The present invention has been made under the aforementioned circumstances and the object of the present invention is to provide a boot, wherein the maximum contraction amount can be more effectively set to be larger and the boot has a predetermined strength.
Another object of the present invention is to provide a seat belt device with the improved restraint performance for the occupant because the maximum contraction amount of the boot is more effectively set to be larger and the boot does not interfere the restraint performance.
Further objects and advantages of the invention will be apparent from the following description of the invention.
To solve the aforementioned problems, a boot according to the first aspect of the invention is disposed between two members, movable relative to each other, and has a flexible portion that contracts when at least one of the members moves to toward the other member, wherein the flexible portion is structured such that sections composing the flexible portion are overlapped with each other during its contraction, and the overlapping direction is perpendicular to the contracting direction.
In the boot according to the second aspect of the invention, the flexible portion is structured such that a cross section of the flexible portion perpendicular to the contraction direction of the flexible portion becomes smaller from one of the members toward the other.
In the boot according to the third aspect of the invention, the flexible portion has convexities and concavities and is structured such that a cross section of the convexity perpendicular to the contraction direction of the flexible portion becomes smaller from one of the members toward the other.
In the boot according to the fourth aspect of the invention, the flexible portion contracts in a telescope-like manner.
In the fifth aspect of the invention, a seat belt device comprises a seat belt; a seat belt retractor for winding up the seat belt for the retraction and withdrawal of the seat belt; an anchor for fixing an end of the seat belt extending from the seat belt retractor to a portion of the vehicle body; a tongue slidably disposed to the seat belt; and a buckle supported by a buckle supporting member fixed to the vehicle body and to which the tongue is latched. Further, the boot as described in one of the first through fourth aspect is disposed between the buckle and the buckle supporting member and/or between the anchor and the end of the seat belt.
In the boot of the present invention having the aforementioned structure, when at least one of two members moves closer to the other, the boot contracts in such a manner that parts composing a flexible portion thereof are overlapped with each other in the direction perpendicular to the contracting direction. Therefore, the boot can contract over a large range regardless of the overlapped parts of the flexible portion, i.e. a thickness of the boot. Accordingly, the maximum contraction amount of the boot can be larger than that of the coventional boot where parts of the flexible portion are overlapped in the contracting direction. In addition, since the boot can contract independently from the thickness of the boot, the wall of the boot can be made to have a specific thickness, thus providing a specific strength.
According to the seat belt device of the present invention, the stroke or movement of at least one of the buckle and the anchor-side end of the seat belt can be increased because the maximum contraction amount of the boot is increased. That is, the maximum stroke or movement of at least one of the buckle and the end of the seat belt to be connected to the anchor can be increased.
Because of the increase in the maximum stroke of the buckle or the anchor-side end of the seat belt, the seat belt extending across the occupant can be pulled further, thereby effectively increasing the restraint force to the occupant by the seat belt and thus significantly improving the restraint performance of the seat belt as compared to the conventional one.